WASHINGTON—A post on a hacker forum popular with cybercriminals has claimed UnitedHealth Group paid $22 million in a bid to recover access to data and systems encrypted by the “Blackcat” ransomware gang, according to two researchers. Neither UnitedHealth nor the hackers involved have commented on the alleged ransom payment, but a cryptocurrency tracing firm partially corroborated the claim on Monday. It is not uncommon for large companies that have been victimized by ransomware gangs to decide to pay the hackers to regain control of their networks, especially in instances where a significant disruption to customers and partners occurred. The forum...